Utility function to enforce docker bridge addr_assign_type

net/bridge.go

@@ -1,7 +1,9 @@
 package net
 
 import (
+	"errors"
 	"fmt"
+	"io/ioutil"
 	"net"
 
 	"github.com/Sirupsen/logrus"
@@ -39,6 +41,40 @@ func DetectBridgeType(weaveBridgeName, datapathName string) BridgeType {
 	}
 }
 
+var ErrSetBridgeMac = errors.New("Setting $DOCKER_BRIDGE MAC (mitigate https://github.com/docker/docker/issues/14908)")
+
+func EnforceAddrAssignType(bridgeName string) error {
+	addrAssignType, err := ioutil.ReadFile(fmt.Sprintf("/sys/class/net/%s/addr_assign_type", bridgeName))
+	if err != nil {
+		return err
+	}
+
+	// From include/uapi/linux/netdevice.h
+	// #define NET_ADDR_PERM       0   /* address is permanent (default) */
+	// #define NET_ADDR_RANDOM     1   /* address is generated randomly */
+	// #define NET_ADDR_STOLEN     2   /* address is stolen from other device */
+	// #define NET_ADDR_SET        3   /* address is set using dev_set_mac_address() */
+	// Note the file typically has a newline at the end, so we just look at the first char
+	if addrAssignType[0] != '3' {
+		link, err := netlink.LinkByName(bridgeName)
+		if err != nil {
+			return err
+		}
+
+		mac, err := RandomMAC()
+		if err != nil {
+			return err
+		}
+
+		if err := netlink.LinkSetHardwareAddr(link, mac); err != nil {
+			return err
+		}
+		return ErrSetBridgeMac
+	}
+
+	return nil
+}
+
 func isBridge(link netlink.Link) bool {
 	_, isBridge := link.(*netlink.Bridge)
 	return isBridge